To produce semiconductor products such as integrated semiconductor circuits, etc., it is generally necessary to repeatedly conduct CVD, etching, etc. to semiconductor wafers, etc. by semiconductor-producing apparatuses, while precisely controlling the amount (trace amount) of a treating gas supplied. For this purpose, for instance, mass flow rate-controlling apparatuses such as mass flow controllers are used (see JP1-227016A, JP4-366725A and JP4-366726A).
The structure of the general mass flow rate-controlling apparatus will be explained referring to FIGS. 11 and 12. FIG. 11 schematically shows one example of a conventional mass flow rate-controlling apparatus arranged on a gas pipe, and FIG. 12 shows a circuit of a flow rate-detecting means in the mass flow rate-controlling apparatus. The mass flow rate-controlling apparatus 2 is disposed in the course of a fluid path (for instance, gas pipe 4) for flowing a fluid such as a liquid, a gas, etc. The semiconductor-producing apparatus connected to one end of the gas pipe 4 is evacuated. The mass flow rate-controlling apparatus 2, comprises a flow path 6 made of, for instance, stainless steel, etc., and both ends of the flow path 6 are connected to the gas pipe 4. The mass flow rate-controlling apparatus 2 comprises a mass flow rate-detecting means 8 positioned on the upstream side of the flow path 6, and a flow rate-controlling valve mechanism 10 positioned on the downstream side of the flow path 6.
The mass flow rate-detecting means 8 comprises pluralities of bypass pipes 12 arranged on the upstream side of the flow path 6. Connected to both ends of the bypass pipes 12 is a sensor pipe 14 for flowing a smaller amount of a gas than in the bypass pipes 12 at a constant ratio. Namely, a predetermined percentage of a gas to the total flow rate always flows through the sensor pipe 14. A pair of series-connected controlling resistor lines R1, R4 are wound around the sensor pipe 14, so that a sensor circuit 16 connected to the resistor lines R1, R4 outputs a mass flow rate signal S1.
The mass flow rate signal S1 is supplied to a controlling means 18 constituted, for instance, by a microcomputer, etc., to determine the mass flow rate (present mass flow rate) of a presently flowing gas based on the mass flow rate signal S1, and control the flow rate-controlling valve mechanism 10 such that the present mass flow rate becomes equal to a mass flow rate of a flow rate-setting signal S0 input from outside. The flow rate-controlling valve mechanism 10 comprises a flow rate-controlling valve 20 disposed on the downstream side of the flow path 6, and the flow rate-controlling valve 20 comprises a diaphragm 22 constituted by a flexible metal plate, for instance, as a valve body for directly controlling the mass flow rate of a gas.
With the diaphragm 22 properly bent toward the valve opening 24, the valve-opening degree of the valve opening 24 can be arbitrarily controlled. To control the valve-opening degree, an upper surface of the diaphragm 22 is connected to a lower end of an actuator 26 constituted by a laminated piezoelectric element, for instance. The entire body of the actuator 26 is contained in a casing 27. The actuator 26 is operated by a valve-operating voltage S4 output from a valve-operating circuit 28 in response to an operating signal from a controlling means 18. The actuator 26 may be an electromagnetic actuator in place of the laminated piezoelectric element.
FIG. 12 shows the relation between the resistor lines R1, R4 and the sensor circuit 16. The series-connected resistor lines R1, R4 are connected to series-connected reference resistors R2, R3 in parallel to form a so-called bridge circuit. A constant current source 30 for supplying a constant current is connected to this bridge circuit. A connection of the resistor lines R1 and R4 and a connection of the reference resistors R2 and R3 are connected to the inputs of a differential circuit 32, which outputs a flow rate signal S1 representing potential difference between both connections.
The resistor lines R1, R4 made of a material whose resistance is variable depending on the temperature are wound around the sensor pipe 14 on upstream and downstream sides, respectively. The reference resistors R2, R3 are kept at a substantially constant temperature.
In the mass flow rate-controlling apparatus 2 thus constructed, when no gas is flowing through the sensor pipe 14, both resistor lines R1, R4 are at the same temperature, resulting in a balanced bridge circuit, so that the potential difference, the output of the differential circuit 32, is zero. When a gas flows through the sensor pipe 14 at a mass flow rate Q, the gas heated by the resistor line R1 on the upstream side flows to a downstream position, at which the resistor line R4 is wound, resulting in the conveyance of heat. As a result, temperature difference is generated between the resistor lines R1 and R4, resulting in resistance difference. The potential difference generated at this time is substantially proportional to the mass flow rate Q of the gas. Accordingly, it is possible to determine the mass flow rate of the gas flowing at this time by adding a predetermined gain to the flow rate signal S1. The valve-opening degree of the flow rate-controlling valve 20 is controlled such that the mass flow rate of the gas being detected becomes equal to that of the flow rate-setting signal S0.
In a general semiconductor-producing apparatus, the gas pipe 4 is sometimes used commonly for various gases. In that case, the gas pipe 4 is branched, with other gases converging in their courses. Flow rate variations by the start and stop of supplying other gases, etc. cause pressure variations, which may be transmitted through the gas pipe 4 to the mass flow rate-controlling apparatus 2, thereby adversely affecting the control of the mass flow rate. Pressure variations may occur by other causes, resulting in deteriorated controllability of the mass flow rate.
JP7-49525U, JP10-268942A and JP2000-137527A propose mass flow rate-controlling apparatuses, in which pressure variations generated on the downstream side are absorbed by ultrasonic nozzles disposed on a fluid outlet or downstream side. Also, JP2003-504888A, JP10-207554A and JP11-259140A propose pressure sensors for detecting the pressure of a gas flow to conduct various treatments based on the gas pressure.
When pressure variation occurs on the upstream side, to which a gas reservoir, etc. is connected, in the mass flow rate controller of JP7-49525U, however, the pressure variation may be directly conveyed to the mass flow rate sensor substantially free from pressure loss, adversely affecting the controllability of the mass flow rate. The mass flow rate-controlling apparatuses of JP10-268942A and JP2000-137527A can absorb pressure variation only in a region meeting the condition of an ultrasonic nozzle, in which pressure upstream of the nozzle is 2 times or more that on the downstream side, but they are even short of controlling the mass flow rate in a region failing to meet the condition of an ultrasonic nozzle.
As shown in FIG. 11, the mass flow rate-controlling apparatus 2 having the mass flow rate-detecting means 8 substantially free from pressure loss on the upstream side should be provided with a regulator for providing a gas flow free from pressure variation to the gas pipe 4 upstream of the mass flow rate-controlling apparatus 2, contributing to the facility cost increase. In addition, JP2003-504888A, JP10-207554A and JP11-259140A do not specifically teach treatment methods of the detected gas pressure, failing to sufficiently eliminate influence on the pressure variation.